Elastomeric fibers are commonly used to provide stretch and elastic recovery in woven and knit fabrics and garments. “Elastomeric fibers” are either a continuous filament (optionally a coalesced multifilament) or a plurality of filaments, free of diluents, which has a break elongation in excess of 100% independent of any crimp. An elastomeric fiber when (1) stretched to twice its length; (2) held for one minute; and (3) released, retracts to less than 1.5 times its original length within one minute of being released. As used in the text of this specification, “elastomeric fibers” should be interpreted to mean at least one elastomeric fiber or filament. Such elastomeric fibers include but are not limited to rubber filament, biconstituent filament and elastoester, lastol, and spandex.
“Spandex” is a manufactured filament in which the filament-forming substance is a long chain synthetic polymer comprised of at least 85% by weight of segmented polyurethane.
“Elastoester” is a manufactured filament in which the fiber forming substance is a long chain synthetic polymer composed of at least 50% by weight of aliphatic polyether and at least 35% by weight of polyester.
“Biconstituent filament” is a continuous filament comprising at least two polymers adhered to each other along the length of the filament, each polymer being in a different generic class, for example, an elastomeric polyetheramide core and a polyamide sheath with lobes or wings.
“Lastol” is a fiber of cross-linked synthetic polymer, with low but significant crystallinity, composed of at least 95 percent by weight of ethylene and at least one other olefin unit. This fiber is substantially elastic and heat resistant.
For woven and knit stretch fabrics, modest proportions of elastomeric fibers are used in combination with relatively inelastic fibers, such as polyester, cotton, nylon, rayon or wool. For the purposes of this specification, such relatively inelastic fibers will be termed “hard” fibers. The proportion of elastomeric fibers in a fabric might vary from about 1% to about 15% by weight to provide desired stretch and recovery properties of the fabric.
In fabrics, elastomeric fibers are used as “bare” fibers or as “covered” fibers, depending on the fabric-making process and the product application. A “covered” elastomeric fiber is one surrounded by, twisted with, or intermingled with hard yarn. The covered yarn that comprises elastomeric fibers and hard yarns is also termed a “composite yarn” in the text of this specification. The hard yarn covering serves to protect the elastomeric fibers from abrasion during weaving and knitting processes. Such abrasion can result in breaks in the elastomeric fiber with consequential process interruptions and undesired fabric nonuniformities. Further, the covering helps to stabilize the elastomeric fiber elastic behavior, so that the composite yarn elongation can be more uniformly controlled during weaving processes than would be possible with bare elastomeric fibers.
Background art processes used for covering elastomeric fibers are typically slow, costly and/or limited in application. These processes include: (a) single wrapping of the elastomeric fibers with a hard yarn; (b) double wrapping of the elastomeric fibers with a hard yarn; (c) continuously covering (i.e., core-spinning) an elastomeric fiber with staple fibers, followed by twisting during winding; (d) intermingling and entangling elastomeric and hard yarns with an air jet; and (e) twisting elastomeric fibers and hard yarns together. FIG. 1A to FIG. 1F are schematic representations of conventionally covered composite yarns, wherein one or more hard yarns cover one or more elastomeric fibers. FIG. 1A shows a hard yarn 1 wrapped around elastomeric fibers 3 (i.e., single-wrapped), and FIG. 1B shows two hard yarns 5, 6 wrapped around elastomeric fibers 7 (i.e., double-wrapped). FIG. 1C shows a core-spun yarn wherein the elastomeric fibers 11 are covered with staple fibers 9. FIG. 1D shows a twisted hard-yarn pair 13, 14 wrapped around elastomeric fibers 15, as accomplished by the Elasto Twist® system of Hamel AG. FIG. 1E shows two hard yarns 17, 19 twisted with elastomeric fibers 21 in a two-for-one twist structure. FIG. 1F shows a multifilament hard yarn 22 intermingled with elastomeric fibers 23, as done in an air-jet covering process.
Operating speeds for these wrapping and twisting processes are typically about 25 meters/minute. The air-jet covering process can be operated at speeds up to 500 meters/minute and more. However, the air-jet covering process is limited to the use of continuous filament hard yarns, wherein the filaments have previously been textured (e.g., false-twist textured). For widely used staple fibers, such as cotton, wool and linen, or for non-textured continuous filaments, the traditional, slower covering methods are currently used.
Knitting processes can use either bare or covered elastomeric fibers to produce stretch knit fabrics for garments. The choice depends on the type of garment and its desired aesthetics and performance in use. However, for weaving processes to make stretch woven fabrics, industry practice is to use the more costly composite yarn (e.g., covered elastomeric fibers) in the warp only, or in the weft only, or in both the warp and the weft.
Further, it is customary in weaving operations to prepare the warp yarns with a coating of size, whether the warp is made from hard yarns or composite yarns. “Size” is an adhesive coating made from materials such as starch or polyvinyl alcohol (PVA). When applied to the warp yarns, size helps to provide a smooth yarn surface and to increase the strength of the warp yarns. In weaving, the warp yarns are subjected to friction and high forces during the action of the shedding mechanisms. Size is used with warp yarns to reduce yarn breaks during processing. Practically all of the size is removed from the yarns during fabric wet-finishing operations.
Background art composite yarns comprised of spun cotton and elastomeric fiber(s) are typically dyed as packages before use in weaving, but there are disadvantages to such dyeing. Specifically, the elastomeric core yarn will retract at the hot water temperatures used in package dyeing. In addition, the composite yarn on the package will compress and become very tight, thereby impeding the flow of dyestuffs into the interior of the yarn package. This can often result in yarn with different color shades and stretch levels, depending on the yarn's diametral position within the dyed package. Small packages are sometimes used for dyeing core-spun composite yarns to reduce this problem. However, small-package dyeing is relatively expensive because of extra packaging and handling requirements.
Although common industry practices are highlighted above, additional background art provides alternative suggestions to improve weaving processes or products. For example, U.S. Pat. No. 3,169,558 discloses a woven fabric with bare spandex in one direction (e.g., warp) and hard yarns in the other direction (e.g., weft). However, the bare spandex must be drawn and substantially twisted in a separate, costly operation prior to using it in the weft or the warp. For example, a 100 dernier bare spandex fiber, drafted 4×, must have 18.25 twists per inch, as a minimum.
Great Britain Pat. No. GB 1513273 discloses a warp-stretch woven fabric and process wherein pairs of warp yarns, each pair having one or more bare elastomeric fibers and a secondary hard yarn, are passed in parallel and at different tensions through the same heald eyelet and dent. Achieving weft stretch by using elastomeric fibers is also described as possible, but by using conventionally-covered composite yarns in the weft. Size is not applied.
Japanese Pat. No. 4733754 discloses a method to manufacture stretch woven fabrics in a way that manages the elongation of sensitive spandex during weaving. An elastomeric strand is lightly wound (wrapped) with a PVA-based fiber strand, and then the two strands are twisted together to form a yarn B. The yarn B can be optionally sized to further arrest stretchability during weaving. The PVA fiber strand is later dissolved during fabric wet processing to provide a stretch product. Further, an elastic yarn C is made by wrapping yarn B with various continuous (synthetic) fiber strands, and then is optionally sized. Both yarns B and C can be used in the warp or weft to provide elastic fabrics. However, this method to make stretch-woven fabrics requires use of composite yarns made by wrapping, as well as optional use of size.
Japanese published Application No. 200213045 discloses a process used to manufacture a warp-stretch woven fabric using both composite and hard yarns in the warp. The composite yarn comprises polyurethane yarn wrapped with a synthetic multifilament hard yarn and then coated with size material. The construction of the composite is that of the composite yarns represented in FIG. 1A and FIG. 1B, before coating with size material. The composite yarn is used in the warp in various proportions to a separate synthetic multifilament hard yarn in order to achieve the desired properties of stretch in the warp direction. This composite yarn and method were developed to manufacture warp-stretch fabrics, and to avoid difficulties in the weaving of weft-stretch fabrics. However, the method is costly as it uses traditional, slow, wrapping processes to cover the polyurethane yarn with a covering of multifilament hard yarn.
Therefore, there is a need in the art to provide “covered” elastomeric fibers that can be: (1) sufficiently protected and stable for use in weaving and knitting operations; (2) applied in a variety of woven and knit fabrics; and (3) applied in manufacturing at higher speeds and lower costs than those produced by background art covering methods.